Solid propellant combustion catalyst



United States Patent SOLID PROPELLANT COMBUSTION CATALYST Theodore A. Burgwald, Hammond, Ind., assignor to Standard Oil Company, Chicago, Ill., a corporation of Indiana No Drawing. Filed Feb. 7, 1955, Ser. No. 486,749

7 Claims. (Cl. 52-.5)

This invention relates to a solid propellant combustion catalyst and it pertains more particularly to an improved gas generating composition for use in jet propulsion.

Jet propulsion of the rocket or assist take-off type is obtained by the burning of combustible components in a gas-producing propellant grain with oxygen also contained therein. A jet engine employs combustion products formed by burning a fuel with air in a gas generator to drive a turbine which, in turn, drives an air compressor for supplying said air to burn said fuel. It is necessary to start the turbine of a jet engine to bring it to required speed and temperature by an auxiliary starter which utilizes a gas-producing grain composition for the production of large volumes of gas at high temperature. The preferred type of grain comprises ammonium nitrate, an organic combustible binder and a catalyst for controlling the rate of combustion under the existing pressure conditions. Catalysts heretofore employed for this purpose, such as ammonium dichromate, iron ferro and ferricyanides (Prussian blues) and the like, have been successfully employed in jet assist take-cit units, rocket propellants, etc., but when grains containing this type of catalyst are employed for starting up the turbine of a jet engine, severe erosion difficulties have been encountered. An object of this invention is to provide an improved catalyst for such grains which will avoid, or at least minimize the erosion difliculties but will, at the same time, give the desired burning rate control under the varying operating pressures encountered. A further object is to provide an improved grain which is useful not only for jet engine startup but also for use as a rocket fuel and for a jet assist take-off unit, which grain is characterized by a burning rate at 1,000 psi, of at least about -.06 inch per second and which is preferably of the order of .1 to .2 inch per second or more and a pressure exponent, as described hereinbelow, is below about .8 and preferably below about .7. Other objects will be apparent as the detailed description of the invention proceeds.

In practicing the invention there is employed as a catalyst, in a grain comprising ammonium nitrate and a combustible plastic binder, about .5 to by weight of a sulfurized substituted diphenylamine blue dye having a color index in the range of 956 to 961, inclusive, which dye preferably contains about 10 to 70% by weight of alkali metal carbonate such as sodium carbonate. In this specification and in the claims based thereon the substituted true indophenoles and the substituted leuco forms thereof are included as substituted diphenylamines. The catalyst may contain small amounts of other salts such 'as sodium chloride, sodium sulfate, etc. It appears that the presence of a small amount, i.e., at least approximately 10% based on total dye, of the inorganic salt such as sodium carbonate is desirable and best results have been obtained with sodium carbonate contents of the order of 10 to 35%.

Grains employing the defined amounts of such catalyst have been found to give markedly superior results in the Ice 2 f starting of jet engines and, particularly, have been found to substantially eliminate erosion difiiculties previously encountered with catalysts heretofore used. While the exact course of erosion and other difiiculties encountered with prior catalysts cannot be defined with certainty, it is believed that the unburned residues from prior catalysts, i.e., chromium oxide, iron oxide, etc., remain as an abrasive solid when expelled through the exit nozzle of the combustion chamber while sodium carbonate and other inorganic material in the improved catalyst is melted and/ or is in non-abrasive form. Furthermore, the amount of inorganic material in the improved catalyst is much less than that which was heretofore required and it is desired that the amount of inorganic material is minimized.

While the blue dye of the invention may be used as the sole combustion or burning rate catalyst, it is preferred to employ it in conjunction with at least one other burning promoter of low ash content such as carbon black. In applications where the erosion problem is not encountered, the blue dye of the invention may be employed in conjunction with Prussian blue, ammonium dichromate or other combustion catalysts, heretofore known to the art, with advantageous results. In other words, the sulfurized substituted diphenylamine blue dye with its contained sodium carbonate is not only a catalyst per se but it is a valuable synergist for known catalysts and other burning rate promoters. In addition, the gasproducing propellant grain composition may contain small amounts of a burning rate modifier, gassing inhibitor, or other component useful in improving the physical characteristics and/or stability of the grain.

The sulfurized substituted diphenylamine blue dye which is employed as a catalyst in this invention may be prepared by heating 10 parts by weight of 2,4-dinitro-4- hydroxy diphenylamine with 18 parts by weight of dry sodium tetrasulfide in 50 to 60 parts by weight of alcohol in an autoclave to a temperature in the range of to l45 C., under a pressure of 8 to 10 atmospheres for a period of 3 to 4 hours. After cooling, the dye may be isolated by distilling off the alcohol or it may be separated in the form of crystals and freed from mother liquor by filtration. Separation of the crystallized dye material may be expedited by the addition of sodium carbonate or sodium bicarbonate as is well known in the dye art. A method of preparation of such dyes is described in US. 665,726 and other methods for preparing dyes of this general type which may be employed in the practice of the invention are described in Color Index, Society of Dyers and Colorists, 1st edition, January 1924, under the specific color indexes. Examples of commercially available sulfurized substituted diphenylamine blue dyes are listed in the Technical Manual and Yearbook of the American Association of Textile Chemists and Colorists (1954) at page 240-1 under headings 956 (Pyrogene Direct Blue), 957 (Immedial Sky Blue), 959 (Immedial lndone), and 961 (Pyrogene Indigo), good results having been obtained with Pyrogene Direct Blue RL-CF (Ciba), Sulfogene Direct Blue BN (DuPont), Pyrogene Blue GLR-CF (Ciba) and Sulfogene Brilliant Blue BGL (DuPont). The blue dyes of color index 956, such as Pyrogene Direct Blue RL-CF, and Sulfogene Direct Blue BN Conc. 200% are preferred.

A concentrated form of such dye is preferred but the dye preferably should contain or be employed with at least about 10% by weight, based on total dye, of an alkali metal carbonate such as sodium carbonate. Usually the commercial dyes contain the required amounts of sodium carbonate and, in some cases it may be desirable to wash the commercial dyes to eifect removal of sodium carbonate down to the preferred level of about 10 to 35%. The excess or at least a part of the inorganic salt such as the carbonate may be removed by washing with water or dilute (about 5%) aqueous solutions of ammonium hydroxide, sodium acetate, ammonium nitrate, or the salts may be removed by dialysis using dilute ammonium hydroxide solution.

The composition of the gas-producing propellant grain of this invention is substantially as follows:

AMMONIUM NITRATE The term ammonium nitrate as used in this specification and in the claims is intended to mean either ordinary commercial grade ammonium nitrate such as conventionally grained ammonium nitrate containing a small amount of impurities which is then generally coated with a small amount of moisture-resisting material such as petrolatum or paraffin, or to mean military grade ammonium nitrate or a mixture of minor amounts (usually less than of other inorganic nitrates such as sodium nitrate or potassium nitrate with the ammonium nitrate. Finely ground ammonium nitrate is preferred in order to reduce the voids to a minimum and hence avoid the use of excess binder material.

BINDER The binder material of the gas-producing propellant composition is a thermoplastic material comprising at least one plasticizable component consisting essentially of a synthetic organic polymeric material plasticized with an oxygen-containing plasticizer.

Examples of such plasticizable materials are cellulose esters, polyvinyl resins such as polyvinyl acetate, polystyrenes, styrene-acrylonitrile copolymers, asphalt and polyamide resins. Mixtures of these polymeric materials may be used. Thus, cellulose acetate may be used either as the sole plasticized polymeric base material or the cellulose acetate may be used along with asphalt, or with cellulose acetate-butyrate. Cellulose acetate-butyrate ester may be used alone or with other polymeric base materials such as polyamide resin-95, with polystyrene, with polyacrylonitrile or with asphalt. The cellulose acetate of this invention is known as partially esterified cellulose acetate having an acetic acid content between 51 and 57% by weight of acetic acid, preferably a lacquer grade which analyzes between 54 and 56% by weight of acetic acid, and having a viscosity when dissolved in acetone between 2 and 80 centipoises at 25 C. at 20% by weight concentration in the acetone solution. The cellulose acetatebutyrate is described as having an acetic acid content between 7 and 55 weight percent and a butyric acid content between about 16 and 61%. As in the case of cellulose acetate, the cellulose acetate-butyrate commercial grades are described by viscosity when dissolved in acetone: 20% by weight of polymer in acetone is used as standard in determining centipoise viscosity. The preferred cellulose acetate polymer has a viscosity between about 10 and 40 centipoises. When used alone the cellulose esters constitute between about 18 and 40% by weight of the binder material, usually from about 25 to about 35%.

Another plasticizable polymeric base material which may be used in the binder is polyvinyl acetate. This polymer may be used as a sole plasticizable base material or it may be used in combination with styrene-acrylonitrile copolymer with or without the presence of asphalt component. It has been found that polyvinyl acetate of commercial grade known as Gelva-800 and also Gelva-lOO and mixtures of these are suitable as binder components in the grain compositions. The styrene acrylonitrile copolymer used in tests described hereinbelow had an acrylonitrile content of 28%. It had a specific viscosity of 1200 determined as a 0.4% solution in dimethyl formamide. The asphalt component of the binder, which for purposes of this specification and claims is defined as polymeric base material and is preferably obtained by oxidation of a petroleum residuum as by blowing with air. A particularly suitable asphalt which was used in formulating asphalt-containing grains described hereinbelow was a roofing and coating grade product obtained by air-blowing a mid-continent petroleum residuum stock. The asphalt had a softening point within the range of 215-235 F., a flash point (Cleveland Open Cup) above 550 F., a penetration of more than 0.8 mm., at 32 F., and less than 4.0 mm., at F. in the A.S.T.M. Penetration Test.

The relative proportions of asphalt to styrene-acrilonitrile copolymer in the binder is preferably within the range of one part by weight of asphalt to 3 parts and 3 parts as asphalt to one part by weight of styrene-acrylonitrile although the combination of these two polymeric base materials may contain as low as one part of asphalt to ten parts of the styrene-acrylonitrile copolymer.

The thermoplastic binder compositions contain in addition to the above synthetic polymeric base material at least one oxygen-containing plasticizer. Since the plasticizer material is usually the predominant component of the binder, cognizance of stoiohiometric oxygen balance is taken in the choice of plasticizer material. Thus, plasticizers which provide a part of the oxygen requirement are generally preferred since substantially smokeless combustion of the explosive composition is highly desirable. Suitable plasticizers for the binder composition may be classified as polymeric esters, esters of polyhydric alcohols, ethers of nitrophenols, nitromonocyclic aromatics, esters of polycarboxylic acids, alkyl ethers of polyglycols, and polyglycols. Illustrative examples of such plasticizers are ethylene glycol diglycolate, acetin (mono, di and tri), nitromethylpropanediol diacetate, triethylene glycol di-2- ethylbutyrate (Flexol 3GH), triethylene glycol di-2- ethylhexoate (Flexol 3G0) and polyethylene glycol di- 2-ethylhexoate known commercially as Flexol 4G0. Specific examples of esters of polycarboxylic acids are the trialkyl citrates such as triethyl citrate and the dialkyl phthalates such as dibutyl phthalate and dioctyl phthalate. Specific examples of nitrophenol ethers are dinitrophenol allyl ether and the nitrodiphenyl ethers such as 2,4-dinitrodiphenyl ether and di(dinitrophenl) triglycol ether which is prepared by reacting triglycol with dinitrochlorobenzene. Such nitromonocyclic aromatics as nitrotoluene, dinitrotoluene, and dinitrobenzene are particularly effective as plasticizers when used in combination with 2,4- dinitrodiphenyl ether to plasticize polymeric base materials such as rnixtures of styrene-acrylonitrile with asphalt.

The use of the combination of these nitro aromatic compounds in forming grains containing any of the above polymeric base materials is particularly desirable since they are elfective in maintaining high burning rates of the compositions.

The plasticizer components of the binder material, of which two or more are preferably used, may make up as much as about 82% of the binder material. Generally, the minimum amount of plasticizer in the binder is not less than about 40% by weight of the binder.

CARBON COMPONENT The carbon component of the gas-producing composition is finely divided carbon which will pass through a #20 US. Standard sieve. Highly adsorptive activated carbons such as Norit and Nuchar, well known in the art as activated carbon made from residual organic material make up one class of effective burning rate components. A second general class of carbon useful for increasing the burning rate of the compositions are the carbon blacks, roughly classified as the channel blacks and the furnace combustion blacks. The carbon blacks are characterized by low ash content, that is, less than 0.5%, usually less than about 0.15%, and by having extremely small particle size, that is, 50 to 5000 A. and contain adsorbed hydrogen and oxygen. However, to avoid dusting and to afford convenience in handling, some carbon blacks are formed to the so-called bead type carbon blacks. The beads are extremely soft and physically unstable and hence become disintegrated during the milling of the composition. Examples of bead type carbon blacks are Micronex Beads (channel blacks) and Statex Beads (furnace blacks).

A third type of carbon which may be used in the composition is finely ground petroleum coke, particularly petroleum coke obtained as residue in the pipestilling of Mid-Continent heavy residuums. Such coke usually contains less than about 1% ash and hence, like the carbon blacks, are particularly suitable for use in gas-producing grains where solid inorganic particles in the combustion gas must be kept to a minimum. The coke may be activated by methods well known to the art to improve the efiiciency thereof as a burning rate promoter and is preferably ground to particle size to pass througuh a #325 US. Standard sieve prior to incorporation in the gasproducing composition.

Still another type of carbon which is useful for improving the burning rate is graphite, flake or amorphous. If derived from a natural graphite, the ash content should be reduced below 5% which can be accomplished by treating the natural product by air-flotation or the ash content may be reduced by leaching with mineral acid or by other methods well known to the art. Graphite of colloidal or semi-colloidal particle size is preferred.

INORGANIC CATALYST As indicated hereinabove, the combustible dye catalyst is used in gas-producing compositions in the absence of inorganic catalyst where inorganic particles are undesirable in the combustion gases produced by the burning grain material. However, in rocket propellant grains and assist-take-olf grain formulations the combustible dye catalyst may be used along with such catalysts as Prussian blue, either of the soluble or insoluble type. These iron-type catalysts are the subject matter of US. patent applications filed by Wayne A. Proell and William G. Stanley, Serial No. 273,564, filed February 26, 1952, and Serial No. 288,065, filed May 15, 1952. Examples of the iron cyanide catalysts, that is Prussian blues, which may be used in the compositions are ferro ferrocyanide, ferric ferrocyanide, ferro ferricyanide, ferric ferricyanide, potassium ferric ferrocyanide, sodium ferric ferrocyanide, ammonium ferric ferrocyanide, potassium soluble Prussian blue, sodium soluble Prussian blue and ammonium-sodium soluble Prussian blue. Ammoniated insoluble Prussian blue catalyst produced by exposing insoluble Prussian blue, that is, ferri ferrocyanide, to contact with ammonia gas as taught in Serial No. 288,549, filed May 17, 1952, by Wayne A. Proell may also be used as the inorganic catalyst in the composition.

Sodium potassium or ammonium chromates and/or dichromates may be employed. Other suitable chromium type catalysts are described in US. patent application, Serial No. 279,698, filed April 1, 1952, by Wayne A. Proell and are the organochromium compounds such as the chromate salts of aliphatic polyamines and cycloaliphatic polyamines, for example, ethylene diamine chromate and dimethyl piperazine chromate. These inorganic catalysts may be used in amounts up to 4% by weight in propellant grain compositions along with the combustible organic dye catalyst.

BURNING RATE MODIFIER For such uses as rocket propulsion, assist take-off service and gas generation for starting up of the turbine of a jet engine, an explosive is desired which has nondetonating characteristics rather than detonating characteristics of ordinary ammonium nitrate explosives. The burning characteristics of most detonating explosives are dependent upon the temperature and pressure in the combustion chamber. The relationship of burning rate and pressure at constant temperature is expressed by R. N. Wimpress in Internal Ballistics of Solid Fuel Rockets,

wherein B is the linear burning rate at pressure p, B is the linear burning rate for the composition at 1000 p.s.i., p is the pressure in p.s.i., in the burning chamber and n" is a pressure exponent showing dependence of the burning rate on pressure. The exponent is the numerical value equal to the slope of the curve of the burning rate in inches per second obtained by plotting the burning rate at various pressures, usually 600 p.s.i. to 1800 p.s.i., on log-log paper. Ammonium nitrate compositions usually have a pressure exponent of about 0.7 or higher. The lower the value of n the less is the detonating character of the decomposition of a gasproducing composition and the more even and smooth is the burning rate of the propellant grain. Thus a sustained thrust rather than a detonation is obtained by smooth burning of the grain and a sustained flow of gas from the gas generator is obtained if the pressure exponent of the composition is low.

A burning rate modifier may be added to the gasforming composition for the purpose of improving the combustion characteristics of the grain material with respect to pressure exponent. It has been found that oximes having the oxime group or groups attached to acyclic carbon atoms in the oxime molecule are particularly eifective for depressing the slope of the burning rate-pressure curve, that is, the pressure exponent. Aliphatic acyclic oximes are preferred but aromatic oximes such as benzaldoxime and salicyaldoxime are effective. Oximes corresponding to the general formula X NOH R( i(CHi) i lR' where R and R are methyl, ethyl or hydrogen, X is oxygen or NOH and y is an integer from 0 to 2, are preferred. Examples of such oximes are acetonylacetone dioxime, acetylacetone dioxime, acetonylacetone monooxime and succinaldehyde doxime. The oxime component is added to the molten binder material prior to the addition of the nitrate, catalyst, and carbon or it may be added during the milling operation to which the ammonium nitrate and binder are subjected as described hereinbelow.

GASSING INHIBITOR It has been discovered that certain aromatic amines when introduced into the ammonium nitrate base grain, particularly such grains containing Prussian blue catalyst and finely divided carbon, have the very desirable characteristic of decreasing the amount of gassing of the compositions in high temperature storage and frequently the presence of these amines in the composition eliminates or essentially eliminates gassing for prolonged periods of time. The aromatic amine gassing inhibitors fall into two main classes. The first class consists of diphenylamine, dinaphthylamine and phenyl naphthylamine. In the case of the naphthylamines, the linkage between the naphthyl radical and the nitrogen may be either alpha or beta. The second group of aromatic amines which are effective as gassing inhibitors is represented by the empirical formula RZ(NR'R")x wherein Z is an aromatic nucleus which may be phenyl or naphthyl, R may be hydrogen or alkyl containing from 1 to 12 carbon atoms, R and R" may be hydrogen or alkyl containing from 1 to 4 carbon atoms and x is an integer from 1 to 3.

Examples of monoamino-containing compounds are: aniline, l-naphthylamine, the toluedenes, the xyladines, dodecyl aniline, N-methyl aniline, N,N-dimethyl aniline, and N-sec-butyl aniline. Diamino compounds which are effective are diamino benzene, diamino toluene, diamino naphthylene, methyl diamino naphthylene dodecyl diamino naphthylene, N-sec-butyl diamino benzene, N,N- di-sec-butyl diamino benzene, N-methyl diamino naphthylene. Examples of triamino compounds which are effective are: triamino benzene, triamino naphthylene, triamino toluene, and triamino methyl naphthylene.

A distinct improvement in the gassing tendency of the composition is obtained by the use of very small amounts of the above amines, that is, as low as .5 by weight of the total composition. In general, it has been found that use of more than about 4% by weight of the amines fails to give additional gassing inhibiting effect.

In addition to the above components there may be added materials such as small amounts of surfactants to the binder material for the purpose of aiding the mixing and milling operation and to obtain better contact of the components in the grain. These surfactants are usually added in amounts not more than about .5 by weight based on the total weight of the grain and they have very little, if any, direct effect on the burning properties of the grain material. An example of such surfactant is Onyxide. Onyxide is an alkenyl dimethyl ethyl ammonium bromide, a cation-active quaternary ammonium salt having surfactant properties.

In preparing the compositions of this invention, the binder material is first prepared and the ammonium nitrate and catalyst are milled with the plasticized binder. The binder is prepared by heating the plasticizer material to a temperature below about 150 C., usually within the range of from about 120 C. to about 140 C. The heated plasticizer material is stirred and the polymeric base material is added, heating and stirring being continued until a homogeneous mixture is obtained. The burning rate modifier, that is, oxime, when added to the composition, is added to this homogeneous plasticized mass and thoroughly stirred therewith before the addition of the ammonium nitrate and the catalyst components of the finished grain.

The blue dye catalyst, with or without carbon, may be thoroughly mixed, with or without the carbon, with the powdered ammonium nitrate before addition to the binder material. On the other hand, the dye catalyst may be added immediately preceding the addition of the ammonium nitrate. The ammonium nitrate and catalyst are then milled in the plasticized mass at a temperature below about 120 C. and preferably at a temperature not in excess of about 110 C. Milling is continued until a product of uniform texture is obtained, after which the material is molded into shaped propellant grains and burning rate test strips at temperatures not in excess of 110 C.

PREPARATION AND TESTING OF BURNING RATE TEST STRIPS In preparing the test strips, the formulated composition is molded at 2000 pounds pressure into rectangular strips of about one inch by three quarters inch cross-sectional dimension. These strips are cut into twelve A" x A" test strips about five inches in length for use in determining burning rates. The strips are provided with drilled holes 3" apart through which are passed fusible wires which are connected to a timing device for obtaining the burning rates.

The test strips are coated with lacquer grade cellulose acetate to inhibit surface burning along the test piece. The test piece is then placed in a pressure bomb and electrical connection of the fuse wires is made to the timing device. The timing device is started by the fusing of one wire and as the test piece burns along its length the timing device is stopped by the fusing of the second wire. Thus the time for burning of 3" of the test piece is obtained. The test piece is ignited by means of a Nichrome resistance wire placed in contact with one end of the test piece. Burning rates for the test pieces are determined at pressures of 600, 800, 1000, 1200, 1400, 1600 and 1800 pounds per square inch nitrogen pressure.

The burning rate in inches per second for the different pressures are plotted on log-log paper and the plot gives a straight-line relationship, the burning rates being plotted vertically and pressures being plotted horizontally. The slope of this straight-line is defined as the exponent of the burning rate as related to pressure in the above formula. Burning rates of the materials in this specification are defined as the burning rates at 1000 pounds nitrogen pressure.

Gas-producing grains are prepared by molding the compositions into cylindrical grains under a pressure of about 2,000 to 4,000 p.s.i. The size and shape of the grains will depend, of course, upon their intended use; for starting a jet engine the grains may be about 3 to 6 inches in diameter and about 3 to 6 inches in length while for assist take-off service the grains may be about 2 to 3 feet in length. The grains are usually provided with a hole or opening extending lengthwise of the grain to provide an aperture which may be circular, starform, cruciform, etc., to afford increased burning surface. Such grains may be mounted in a conventional case and may be ignited or fired by electrical or other known means. The combustion gases produced by firing of the grain may be of the order of 1,500 to 2,500 F., and the pressure or impulse produced by the hot gases will, of course, be dependent upon the grain size, diameter of the nozzle, etc. When employed in assist take-01f service the nozzle may be a part of the grain case. When employed for starting a jet engine, the nozzle may be incorporated in a breech assembly in the motor itself. Since no novelty is claimed in the method of using or firing the grain, no further description thereof is necessary.

Gas-producing grains for airplane assist take-off service are prepared in a manner similar to the above. These may be provided with centrally located holes of different shapes, that is starform, cruciform or circular. Such grains are usually of greater length than diameter, that is about 30 in length by 3" in diameter. The grain compositions may also be molded into disc form, stacks of the discs being used as gas-forming propellant material for rockets.

The following test series illustrate the catalytic effect of the dyes in promoting the combustion of the gas-forming grains.

Test Series A A binder material was prepared by heating at about 140 C. 9.6 parts by Weight of 2,4-dinitrodipheny1 ether in admixture with 9.6 parts by weight of ethylene glycol diglycolate prepared by condensing 1.2 mols of ethylene glycol with 1 mol of diglycolic acid as taught in the copending application of Norman J. Bowman and Wayne A. Proell entitled Polyester Plasticizer, Serial No. 471,- 992, filed November 30, 1954. To the molten mixed plasticizer was added 5.8 parts by weight of lacquer grade cellulose acetate having an acetic acid content between about 54% and 56% by weight and the mixture was stirred until a homogeneous plasticized material was obtained. The temperature of the plastic mass was lowered to C. and a mixture containing 73 parts by weight of powdered ammonium nitrate and 2 parts by weight of Prussian blue catalyst was added to 25 parts by weight of the molten binder material. The mixture was stirred and then milled to obtain a homogeneous plastic grain material and the burning test strip was prepared and tested as described hereinabove. The grain material had a burning rate of 0.10 inch per second at 1000 p.s.i. and a pressure exponent of 0.72. Substitution of of the binder material with Pyrogene Direct Blue RL-CL (Color Index 956) to give a grain composition consisting, on a weight basis, of 5.18% cellulose acetate, 8.66% 2,4-dinitrodiphenyl ether, 8.66% ethylene glycol diglycolate, 2% Prussian blue catalyst, 2.5 of the blue dye and 73% of the ammonium nitrate gave a composition having a burning rate of 0.14 inch per second at 1000 p.s.i., and a pressure exponent of 0.70, representing a 40% increase in burning rate over the material containing no dye material. A grain material wherein Pyrogene Blue GLR-CI. (Color Index 959) was substituted for 10% of the binder material, the composition of the grain being otherwise the same as the above grain material, had a burning rate of 0.13 inch per second at 1000 p.s.i., and a pressure exponent of 0.73, thus indicating anincreased burning rate of 30%.

A grain composition was fabricated from the same components and by the same procedure as above except that a different ammonium nitrate and 3% by weight of Prussian blue having a burning rate comparable with the dynamite grade was used along with 2.5% by weight of Pyrogene Blue RL-CF and 1% of carbon black (Micronex Beads). The grain composition consisted, on a weight basis of 4.6% cellulose acetate, 7.70% of ethylene glycolate, 7.70% of dinitrodipheny-l ether, 3% Prussian blue, 1.0% carbonblack, 2.5% Pyrogene Direct Blue RL-CF and 73.5% ammoniumnitrate. Upon testing this composition it was found to have a burning rate of 0.19 at 1000 p.s.i., and a pressure exponent of 0.70, thus indicating an increase of 90% over a similar grain composition containing no blue dye catalyst and no carbon black. The carbon black was added to the binder material, mixed with the ammonium nitrate.

Test Series B In another series of experiments, tests were made to examine the catalytic effect of other blue dyes prepared by sulfurizing substituted diphenylamines. Grain compositions were prepared containing the same cellulose acetate, ethylene glycol diglycolate, 2,4-dinitrodiphenyl ether binder material as in Test Series A and substituting for a part thereof, different dyes. A grade of ammonium nitrate having a lower burning rate was used in the compositions. The control composition containing no dye material contained, on a weight basis, 5.8% cellulose acetate, 9.6% ethylene glycolate, 9.6% 2,4-dinitrodiphenyl ether, 2% Prussian blue catalyst and 73.0% ammonium nitrate. This composition was tested and had a burning rate of 0.08 inch per second at 1000 p.s.i., and a pressure exponent of 0.68. Substitution of 10% of the binder with difierent blue dye materials to give grain compositions containing 2.5% by weight of the dye catalyst are tabulated below with burning rates and pressure exponents of the compositions.

1 Color index number.

The results of the burning tests indicate substantial increase in burning rate over the burning rate of the composition containing no dye as catalyst component. A grain composition of similar composition consisting on a weight basis of 6.6% of the cellulose acetate, 5.7% ethylene glycol diglycolate, 7.7% 2,4-dinitrodiphenyl ether, 2% Pyrogene Direct Blue RL-CF of color index 956, 2%

10 carbon black (as substitute for Prussian blue catalyst) and 74% of ammonium nitrate showed a burning rate at 1000 p.s.i., of, 0.09 and a pressure exponent of 0.74. The

test shows that the cooperating carbon black-dye catalyst produces burning rates in this type composition which is of the magnitude satisfactory for jet engine turbine starter, gas-forming compositions.

Test Series C A series of burning rate tests of ammonium nitrate grains was made according to the procedure of Test Series A wherein the binder material consisted of mixtures of the above described asphalt and styrene-acrylonitrile copolymer plasticized with dinitrotoluene and 2,4-dinitrodiphenyl ether. Such compositions will not burn in the absence of a combustion promoter catalyst. A composition consisting of 6.0% asphalt, 4.0% styreneacrylonitrile copolymer, 5.9% 2,4-dinitrodiphenyl ether, 4.1% dinitrotoluene, 4.0% Pyrogene Direct Blue RL-CF and 76% ammonium nitrate had a burning rate of 0.10 inch per second anda pressure exponent of 1.0. A similar composition consisting of 5.6% asphalt, 3.7% styrene-acrylonitrile copolymer, 5.4% 2,4-dinitrodiphenyl eher, 3.8% dinitrotoluene, 3.0% Pyrogene Direct Blue RL-CF, 3.0% carbon blackand 75.5% of the same nitrate had a burning rate of 0.11 inch per second at 1000 p.s.i., and a pressure exponent of 0.64. A grain composition substantially the same with respect to the proportions of these binder components and the same ammonium nitrate which also contained 3% of the carbon black but no dye catalyst had a burning rate of 0.05 inch per second at 1000 p.s.i., and a pressure exponent of 0.74.

In another test the relative amounts of asphalt and styrene-acrylonitrile copolymer and binder composition were changed. A composition consisting on a weight basis of 8.6 styrene-acrylonitrile copolymer, 1.1% asphalt, 4.3% triethyl citrate, 4.3% di(dinitrophenyl) triglycol ether and 3.2% 2,4-dinitrodiphenyl ether as binder material, 1.5% Pyrogene Direct Blue RL-CF, 3% carbon black and 74.0% of the ammonium nitrate had a burning rate of 0.12 inch per second at 1000 p.s.i., and a pressure exponent of 0.67. The control composition containing no dye catalyst, but only the 3% carbon black as catalyst, had a burning rate of 0.04 at 1000 p.s.i.,

and a pressure exponent of 0.71. Thus, even at relatively In still another test a composition consisting of a binder of polyvinyl acetate plasticized with Flexol GH (triglycol dihexoate) and 2,4-dinitrodiphenyl ether and ammonium nitrate mixed with carbon black was examined. The control composition consisting of 4.8% polyvinyl acetate, 3.6% Flexol 3GH, 3.6% 2,4-dinitrodiphenyl ether, 3% carbon black and 85.0% ammonium nitrate had a burning rate of 0.07 inch per second at 1000 p.s.i., and a pressure exponent of 0.68. A similar composition containing only2% by weight of the carbon black and 3% by weight of Pyrogene Direct Blue RL-CF and 83.0% of the ammonium nitrate with the same binder material had a burning rate of 0.11 inch per second at 1000 p.s.i., and a pressure exponent of 0.72.

Having thus described the invention, what is claimed 1s:

1. A gas-.producingpropellant grain consisting essentially of between about 70 and by weight of ammonium nitrate between about 10 and 25% by weight of a combustible plastic binder, which binder consists essentially of (a) synthetic resin selected from the class consisting of cellulose acetate, cellulose acetate butyrate, polyvinyl acetate, polystyrene, poly-acrylonitrile, styrene acrylonitrile and asphalt and (b) a plasticizer selected from the class consisting of ethylene glycol diglycolate, monoacetin, diacetin, tn'acetin, nitromethylpropanediol diacetate, triethylene glycol di-Z-ethyl-butyrate, triethylcne glycol di-Z-ethylhexoate, polyethylene glycol di-2-ethylhexoate, tri-lower-alkyl citrates, di-lower alkyl phthalates, dinitrophenol allyl ether, dinitrodiphenyl ether, di(dinitrophenyl)triglycol ether, nitrotoluene, dinitrotoluene, and dinitrobenzene and between about 0.5 and 5% by weight of an ammonium nitrate combustion catalyst consisting essentially of sulfurized diphenyl amine blue dye having a Color Index in the range of 956 to 961.

2. A shaped gas-producing propellant grain consisting essentially of about 70 to 90% by weight of ammonium nitrate about 10 to 25% by weight of a combustible plastic binder consisting essentially of cellulose acetate plasticized with at least one plasticizer selected from the class consisting of ethylene glycol diglycolate, monoacetin, diacetin, triacetin, nitromethylpropanediol diacetate, triethylene glycol di-2-ethylbutyrate, triethylene glycol di-2- ethylhexoate, polyethylene glycol di-Z-ethylhexoate trilower-alkyl citrates, di-lower-alkyl phthalates, dinitrophenol allyl ether, dinitrodiphenyl ether, di(dinitrophenyl) triglycol ether, nitrotoluene, dinitrotoluene, and dinitrobenzene, about 1 to 5% by weight of carbon black and an ammonium nitrate combustion catalyst consisting essentially of .5 to 5% of a sulfurized diphenylamine blue dye having a Color Index of 956, said dye containing from about 10 to 70% by weight of sodium carbonate based on the dye component.

3. The composition of claim 1 which contains about 10 to 70 weight percent of alkali metal carbonate based on said dye.

4. The composition of claim 1 which includes about .5 to 4% of a Prussian blue catalyst.

5. The composition of claim 4 wherein said Prussian blue catalyst is insoluble Prussian blue.

6. The composition of claim 1 which contains about 1 to 5% of carbon black.

7. The composition of claim 1 which includes about 1 to 5% of carbon black and about .5 to 4% of Prussian blue.

References Cited in the file of this patent UNITED STATES PATENTS 2,440,327 Crawford Apr. 27, 1948 2,479,470 Carr Aug. 16, 1949 FOREIGN PATENTS 655,585 Great Britain July 25, 1951 485,661 Canada Aug. 12, 1952 

1. A GAS-PRODUCING PROPELLANT GRAIN CONSISTING ESSENTIALLY OF BETWEEN ABOUT 70 AND 90% BY WEIGHT OF AMMONIUM NITRATE BETWEEN ABOUT 10 AND 25% BY WEIGHT OF A COMBUSTIBLE PLASTIC BINDER, WHICH BINDER CONSISTS ESSENTIALLY OF (A) SYNTHETIC RESIN SELECTED FROM THE CLASS CONSISTING OF CELLULOSE ACETATE, CELLULOSE ACETATE BUTYRATE, POLYVINYL ACETATE, POLYSTYRENE, POLY-ACRYLONITRILE, STYRENE ACRYLONITRILE AND ASPHALT AND (B) A PLASTICIZER SELECTED FROM THE CLASS CONSISTING OF ETHYLENE GLYCOL DIGLYCOLATE, MONOACETIN, DIACETIN, TRIACETIN, NITROMETHYLPROPANEDIOL DIACETATE, TRIETHYLENE GLYCOL DI-2-ETHYLBUTYRATE, TRIETHYLENE GLYCOL DI-2-ETHYLHEXOATE, POLETHYLENE GLYCOL DI-2- ETHYLHEXOATE, TRI-LOWER-ALKYL CITRATES, DI-LOWER ALKYL PHTHALATES, DINITROPHENOL ALLYL ETHER, DINITRODIPHENYL ETHER, DI(DINITROPHENYL) TRIGLYCOL EHTHER, NITROTOLUENE, DINITROROLUENE AND DINITROBENZENE AND BETWEEN ABOUT 0.5 AND 5% BY WEIGHT OF AN AMMONIUM NITRATE COMBUSTION CATALYST CONSISTING ESSENTIALLY OF SULFURIZED DIPHENYL AMINE BLUE DYE HAVING A COLOR INDEX IN THE RANGE OF 956 TO
 961. 